The glycosyltransferases are a family of intracellular membrane-bound enzymes that participate in the coordinate assembly of the carbohydrate moieties of glycoproteins and glycolipids. The localization of glycosyltransferases on the cell surface and their functional role in intercellular recognition and adhesion has been postulated. The important biosynthetic role of the intracellular glycosyltransferases is well documented. In contrast, the existence of cell surface glycosyltransferases, their relationship to their intracellular counterparts, and their role in intercellular recognition and adhesion is a subject of controversy. We have developed and characterized a polyclonal antiserum and monoclonal antibodies (McAbs) against bovine UDP-galactose:N-acetylglucosamine galactosyltransferase (GT). Using this polyclonal antiserum, which is cross-reactive with GT from many mammalian species including rat, mouse, and man, a cell surface GT has been demonstrated on a variety of tissue culture cells. Using the McAbs, four unique structural/ functional domains have been defined within the soluble GT polypeptide. In addition, several of these McAbs appear to be able to discriminate between the cell surface GT and the intracellular Golgi-associated GT. Using these highly specific and complementary immunological probes for both the soluble and membrane-bound GT we will continue to: (1)\chemically characterize the cell surface GT on tissue culture cells by a combination of immunopurification and structural analysis; and (2)\to determine, by blocking experiments with monovalent antibody, if this cell surface GT is functionally involved in intercellular recognition and adhesion. (A)